Periodic Table: Classifications — How did Dmitri Mendeleev originally organize the periodic table?

• A. By arranging elements in order of increasing atomic number and grouping elements into periods based on electron configurations
• B. By grouping elements strictly by state of matter at room temperature (solids, liquids, gases)
• C. By arranging elements in alphabetical order by element name and grouping them by common ion charge
• D. By arranging elements in order of increasing atomic mass and grouping those with similar chemical properties, leaving gaps for undiscovered elements

Answer: (D)

Verified step by step guidance

1. Understand the historical context: Dmitri Mendeleev developed the periodic table before the discovery of atomic number and electron configurations, so he could not have used these modern concepts to organize elements.
2. Recall that Mendeleev arranged elements primarily by increasing atomic mass, which was the best measurable property available at the time to order elements systematically.
3. Recognize that Mendeleev grouped elements with similar chemical properties into columns (groups), which allowed him to identify patterns and predict properties of undiscovered elements.
4. Note that Mendeleev intentionally left gaps in his table where no known elements fit the pattern, predicting the existence and properties of elements yet to be discovered.
5. Summarize that Mendeleev's original organization was based on increasing atomic mass combined with grouping elements by similar chemical behavior, rather than atomic number, state of matter, or alphabetical order.